A stupid person. Literally a wasted load of semen. As if to say that they shouldn't have been born. That they should have been wiped away, thrown into the garbage, or washed down the shower drain.
The type of person who creates an UrbanDictionary definition specifically to insult a specific person or group, rather than post an actual definition for the word.
Some fuckwad thought it would be funny to waste a definition for this word to spew an ad hominem about the book Liberal Fascism? Why, he's an even bigger fuckwad than the guy who posted a definition of Moonbat that insulted conservatives.